This invention relates to communications systems and more specifically to an integrated digital multi-channel communications system for operation with multiple mobile units, dispatch agencies, communications channels, and methods.
Mobile communications systems are used in many applications such as police and fire department dispatching and now in such new applications as control of transit bus systems and other municipal government functions. These new communications requirements are leading to the development of integrated local government communications systems.
Conventional communications systems in use in such applications as local governments include mobile users and dispatch agencies that operate on a small number of channels, sometimes as few one or two, with one or two tower sites usually over voice channels only while some systems are now offering data communications. Mobile users communicate with their dispatch agencies over these channels using their system tower sites. Automatic routing of messages between users is not available in these conventional communications systems. If the loading on channels becomes excessive, users are asked to move to alternate channels and if the range from a mobile unit to the tower site becomes excessive, the users must manually switch over to another tower site if available.
The new applications of communications to such requirements as integrated local government systems have increased the need to support large fleets of 4000 vehicles or more over large geographical areas. With the increase in the number of mobile and dispatch agency users, the need to effectively increase the capacity of the communications system by utilizing more channels has arisen. When channel capacity has reached overload conditions, mobile units must be handed off to other channels to balance the channel loading. When mobile units exceed the range of fixed station or tower sites, the mobile unit must be handed off to another tower site with the needed coverage. These hand-offs must be done automatically without loss of messages and be transparent to the users.
The predominant form of communications with most previous communications systems is voice. Voice communications are slow and require a voice channel for each user. The number of voice communications channels must be reduced while increasing the rate of information transfer. To do this digital communications methods must be developed that enable rapid transfer of data over a limited number of channels.
Currently local government agencies have a large variety of existing communications systems that must be supported due to the high cost of replacing these systems. The mobile units must also interface alternate forms of communications such as cellular phone systems. In addition a multiple local government agencies require communications through a single common communications system to reduce infrastructure costs.
Integrated local government communications systems require reliable operation for the safety of the system users and the public being served. The communications system must be reliable and provide failsafe capabilities.
Accordingly a new multi-channel communications system is needed to meet the current and future needs of users in such applications as integrated local governments.